- Any unresolved or continuing solicited or unsolicited Grade 2 or greater severity adverse events, including reactogenicity events, that have occurred since receipt of Dose 1 without a clear, alternative etiology. Unresolved or continuing Grade 1 adverse events are permissible unless, in the opinion of the site principal investigator or appropriate sub-investigator, they would render vaccination unsafe, would interfere with the evaluation of responses or are not generally seen in "normal, healthy subjects".